1. Field of the Invention
This invention relates to an electric power distributor for use in a motor vehicle adapted to distribute electric power supplied from a power source such as a battery incorporated in the motor vehicle to a plurality of electric load units equipped in the motor vehicle.
2. Description of the Related Art
Heretofore, there has been known an electric connecting box, as a device for distributing electric power supplied from a power source incorporated in a motor vehicle to a plurality of electric load units equipped in the vehicle. The electric connecting box is constructed in such a manner that a number of substrates each mounted with a bus bar are placed one over another to form a distributing circuit, and various elements such as a fuse and a relay switch are provided on the circuit.
Recently, an electric power distributor has been developed to make such an electric connecting box smaller and to accomplish a high-speeding switching control. Such an electric power distributor has an arrangement in which semiconductor switching elements such as field effect transistors (FETs) are provided between input terminals and output terminals of the power distributor in place of a relay switch to allow a control circuit of a control circuit board to control on and off of electric current supply.
For instance, Japanese Unexamined Patent Publication No. 10-126963 discloses an arrangement of such a power distributor in which a plurality of semiconductor switching elements or chips are mounted on a control circuit board, current on/off control terminals or control signal input terminals of the semiconductor switching elements are connected to a control circuit of the circuit board, input terminals provided at an appropriate position of the respective semiconductor switching elements for supplying electric current are connected to a power source via a common input terminal connected to the power source whereas output terminals provided at an appropriate position of the respective semiconductor switching elements for outputting power are connected to respective electric load units via output terminals connected to the power source.
In the arrangement of the above publication, the semiconductor switching elements are mounted on the control circuit board. This arrangement makes it difficult to release heat of the semiconductor switching elements, namely, to cool the semiconductor switching elements. In a worse case, it is highly likely that other circuit elements on the same control circuit board may be subjected to adverse affect of the heated semiconductor switching elements. Particularly, in an electric power distributor in which semiconductor switching elements are arranged on a power supply circuit connecting a power source and electric load units, a large amount of heat is expected to generate from the semiconductor switching elements. Mounting such semiconductor switching elements on the control circuit board without any measures is not desirable as mentioned above.
As means for eliminating the above drawback, there has been proposed an arrangement as disclosed in, e.g., Japanese Unexamined Patent Publication No. 10-150283. This publication discloses that each semiconductor switching element are disposed away from a control circuit board in a housing and that the semiconductor switching elements and the control circuit board are electrically connected by connecting means. Each semiconductor switching element are connected to a metallic heat releasing member provided on an outer surface of the housing in such a manner that heat of the semiconductor switching elements is transferable to the heat releasing member, whereby the heat of the semiconductor switching elements is released outside of the housing.
The above arrangement, however, fails to effectively suppress a rise of an ambient temperature in the housing in the case where the air inside the housing is heated resulting from the heated semiconductor switching elements, although the arrangement is effective in lowering the temperature of the semiconductor switching elements themselves by the heat releasing member to some extent. In particular, in an electric power distributor for use in a motor vehicle, the parts are sealably accommodated in the housing to prevent intrusion of rainwater and the like. Therefore, heat inside the housing is not easily released outside once heat is generated in the housing. It is highly likely that a rise of an ambient temperature in the housing may adversely affect performance of other electronic devices, especially, a device of a low heat resistance, in the housing.
It is an object of the present invention to provide an electric power distributor for use in a motor vehicle that is free from the problems residing in the prior art.
It is another object of the present invention to provide an electric power distributor for use in a motor vehicle that enables to suppress a rise of an ambient temperature in a housing with a simplified construction while cooling semiconductor operative elements.
According to an aspect of the present invention, an electric power distributor mountable on a motor vehicle for distributing power from a power source installed in the motor vehicle to a plurality of electric load units equipped in the vehicle comprises: a plurality of semiconductor operative elements which are incorporated in a power supply circuit from the power source to the electric load units; a control circuit board incorporated with a control circuit for controlling an operation of the semiconductor operative elements; a housing for accommodating the semiconductor operative elements and the control circuit board; and a heat releasing member provided on an outside of the housing to release heat from an inside of the housing to an outside of the housing. The control circuit board is arranged over the semiconductor operative elements, and is formed with a heat transfer layer on a surface of the control circuit board that faces the semiconductor operative elements. The heat transfer layer and the heat releasing member are connected with each other by a heat transfer member.
These and other objects, features and advantages of the present invention will become more apparent upon a reading of the following detailed description and accompanying drawing.